Still Firebrand healer (me) when we do it too. We cleared Toth and Zorn the first week 1.2 hit the live servers, but we were stuck on the tanks until just a week ago. Turned out it really was just a lack of dps (we're a fairly casual guild). We kept hittng a second double destruction. As a scoundrel, I do ~200dps averaged over the fight with just vital shot and white damage in between heals. It doesn't sound like a lot but I worked it out and it's about 10 seconds shaved off the fight, and if dps is struggling, every little bit counts.
By having the single target healer DPS during the first phase and burst heal tanks when needed. It can give that little bit of extra damage needed to beat the second DD orbs. If that happens then healing through the defensive phase is a joke and everyone can come out of it topped off allowing the same healer to DPS again. This basically creates a snowball effect that can make the fight incredibly easy when shooting for the first time kill.